In water conservation systems wherein irrigation canals and ditches are utilized for conveying water, it is essential that the surface of the pond, canal or ditch be covered so as to prevent loss of water by drainage or seepage which would otherwise occur through the soil. Application of such covering material to prevent erosion of soil may also be desirable in some instances. Further it is also desirable to provide protective linings for pits, ponds or lagoons containing chemicals such as acids, bases or brines and for structures such as dams.
To that end, one expedient heretofore employed has been cement concrete lining in a layer of about 3 inch/7.6 cm thickness. Another material that has been used for this purpose is so-called asphalt plank which comprises sheets or boards, about 1/2 inch/1.25 cm thick, formed from wood or other cellulosic fiber and saturated with asphalt. Both of these lining materials are relatively costly and entail a somewhat cumbersome procedure for application and use.
Another lining material used for this purpose is prepared from a film or sheet of a solid chlorinated olefin polymer prepared by the suspension chlorination of an olefin polymer, such as polyethylene, having a substantially linear structure. This material is disclosed in Canadian Pat. No. 833,665. Such materials, however, suffer from deficiencies in dimensional stability, i.e., resistance to shrinkage when exposed to high temperatures for prolonged periods of time, and further fail to provide optimum strength and flexibility as measured by modulus and elongation as well as tensile and tear strengths. As a means of overcoming such deficiencies, laminate films structures have been utilized comprising opposed outer layers of such chlorinated polyolefin materials, e.g., chlorinated polyethylene, in conjunction with an internal layer of polyethylene. Such structures have also failed to provide required dimensional stability in combination with desired modulus, elongation, tensile strength and resistance to tear and delamination. A comparison of the data set forth in Table II hereinafter illustrates the problems inherent in such prior known materials and the advantages obtainable by practice of the present invention. As an alternate means of overcoming the aforementioned deficiencies, laminate film structures have been utilized comprising opposed outer layers of such chlorinated polyolefin materials, e.g., chlorinated polyethylene, in conjunction with an internal layer of fabric. Such structures are subject to delamination because the fabric at the unsealed edges of the laminate tends to act as a wick to draw moisture into the laminate. A further shortcoming of the fabric reinforced laminates is that they lack dimensional yield and are therefore subject to failure or separation at joints or welds upon application of lateral stress.